1. Field of the Invention
The present invention relates to magnetic materials comprising at least one rare earth element, iron, nitrogen and hydrogen and bonded or sintered magnets obtained therefrom and processes for preparing the same.
2. Description of the Prior Art
Magnetic materials and permanent magnets are one of the important electric and electronic materials employed in a wide range of from small magnets for various motors and actuators to large magnets for magnetic resonance imaging equipment. In view of recent needs for miniaturization and high efficiency, there has been an increased demand for rare earth permanent magnets of samarium-cobalt (Sm-Co) and neodymium-iron-boron (Nd-Fe-B) systems due to their high efficiency. The Sm-Co permanent magnets are now practically used and one composition of them having a high efficiency shows a high maximum energy product [herein "(BH).sub.max "] of 29.6 MGOe and a Curie temperature (herein "Tc") of 917.degree. C. In order to develop a magnetic material containing less or no Sm and Co which are less abundant resources, permanent magnets of the Nd-Fe-B system are provided and the saturation magnetization (herein "4.pi.Is" or ".sigma.s") of one composition in single crystal reaches 16 KG with a (BH).sub.max of about 40 MGOe, but the Tc is as low as 312.degree. C. and the resistance to oxidation is not sufficient. Accordingly, the incorporation of Co with the Nd-Fe-B system is tried to increase the Tc but with a decreased intrinsic coersive force (herein "iHc"). Further, the incorporation of Co and Al or Ga with the Nd-Fe-B system is tried to give a permanent magnet having a Tc of 500.degree. C. and a (BH).sub.max of 35 to 40 but the resistance to oxidation is still not enough, and for practical purposes the treatment such as ion coating and plating is required.
Further, many studies are conducted on iron nitride having a high 4.pi.Is in the form of a thin film for magnetic recording media or magnetic head materials. However, iron nitride has a low iHc and is difficult to be used as a bulk permanent magnetic material. Thus, in order to increase an iHc, the incorporation of nitrogen as a third component with rare earth-iron (R-Fe) alloys is tried but sufficient magnetic properties have not been obtained. Also, the incorporation of hydrogen with the R-Fe alloys is studied and the increase in 4.pi.Is is observed but such R-Fe alloys containing hydrogen which can be used as permanent magnetic materials have not been obtained.
The magnetic properties of the magnetic materials, bonded magnets and sintered magnets include, herein, saturation magnetization (herein "4.pi.Is" or ".sigma.s"), residual magnetization (herein "Br"), intrinsic coercive force (Herein "iHc"), magnetic anisotropy, magnetic anisotropy energy (herein "Ea"), loop rectangularity (herein "Br/4.pi.Is"), maximum energy product (herein "(BH).sub.max "), Curie temperature (herein "Tc") and rate of thermal demagnetization.